Minimizing solvent waste in catalytic reactions in highly recyclable hydrocarbon solvents†
This paper describes chemistry using organocatalysts in hydrocarbon solvents that minimizes solvent waste by using inexpensive, non-volatile, relatively inflammable, and easily recyclable poly(α-olefin)s (PAOs) as hydrocarbon solvents. These studies show that when substrates have limited solubility in PAO solvents, this issue can be addressed by adding a small amount of a cosolvent. Kinetic studies were also carried out and show that reactions carried out in PAOs are kinetically comparable to reactions in conventional non-recyclable hydrocarbon solvents. A range of strategies that separate and isolate products from reactions in PAOs using a polyisobutylene (PIB)-supported DMAP catalyst have been studied using four different catalytic reactions. In the most general procedure, the PAO phase containing a PIB-bound catalyst is separated from products by low energy liquid/liquid gravity separation. This can be accomplished using a minimal amount of a polar solvent. In another example, the product's low solubility leads to it precipitating during the reaction. In this case, a simple filtration recycles the PAO and a PIB-bound DMAP catalyst. We have demonstrated that the PAO phase containing a PIB bound DMAP catalyst can be recycled for at least 10 cycles without loss of activity. Our studies further showed that leaching of the PAO phase into polar solvents was orders of magnitude less than conventional hydrocarbon solvents such as heptane. The result is that the overall solvent waste generation is lower than for the same reaction carried out in conventional solvents.
- This article is part of the themed collection: Synthetic methodology in OBC